- - Thursday, April 10, 2014

Some comedy aficionados and fans of late-night talk are in mourning over David Letterman’s announcement that he will retire from the “Late Show” in 2015. His departure would leave conservatives breathing sighs of relief if he were not to be replaced by someone who tilts even further left.

Since the days of Steve Allen and Jack Parr, the kings of late-night television have lampooned politicians and the two political parties as the deserving butts of their jokes. Mr. Letterman himself was funnier before he decided to be less entertainer and more political partisan. Some of his rants invite envy from the likes of Chris Matthews and Rachel Maddow of MSNBC. It’s not easy to channel Will Rogers.

Mr. Letterman used an interview with former President Jimmy Carter to invite a “global mandate” to end global warming. He praised Mr. Carter for installing solar panels on the White House roof and subtly and falsely suggested that Ronald Reagan removed them because he didn’t “want to upset the petrol lobbyists.”

In separate interviews with Brian Williams of NBC and Bill O’Reilly of Fox News, Mr. Letterman suggested that President Obama isn’t getting the credit he deserves for his accomplishments. He couldn’t say, exactly, what those accomplishments are. But we can guess. He called Mitt Romney a “felon,” praised Obamacare and calls his colleague Rachel Maddow “the smartest person on television.” Perhaps not a high bar. Mr. Letterman berated several Republican senators, including Rand Paul, Jeff Flake, James M. Inhofe and Ted Cruz for opposing gun-control schemes.

In 2009, he joked that baseball star Alex Rodriguez had “knocked up” Sarah Palin’s 14-year-old daughter, and likened the former governor of Alaska and Republican candidate for vice president to a “slutty flight attendant.” Some joke, and no wit.

Mr. Letterman’s federal campaign-finance disclosures reveal that his liberal politics aren’t an act. With wife Regina, he has given exclusively to Democrats, including Sen. Al Franken, once an unfunny “Saturday Night Live” writer and ape impersonator. Paul Shaffer, leader of the studio band, is also a contributor to the Democrats. When Mr. Letterman leaves, “Late Night” promises to tilt so far to the left everyone will be on the floor.

Stephen Colbert’s show, “The Colbert Report,” is a satire of conservative talk shows, with Mr. Colbert playing a buffoonish caricature of a Republican talking head. Mr. Colbert’s campaign contributions have been to Democratic candidates, and some to his sister, Elizabeth Colbert-Busch, the Democratic nominee for a South Carolina congressional seat. Fame is not easily transferable. Despite help from her famous brother, she lost to Rep. Mark Sanford.

With Mr. Letterman’s departure, some conservative dreamers hoped CBS would replace him with someone who could resist using the show as a political platform.

The network is certainly within its rights to lend itself to Democratic and liberal causes, just as Fox News defines “fair and balanced” in its own way. But when the broadcast networks can’t get beyond partisanship, the entertainment doesn’t entertain. Too bad. Exploiting the gift of “seeing ourselves as others see us” could make everybody laugh.